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78 yamaha 650 special issues

1902 Views 8 Replies 9 Participants Last post by  choober
My 78 yamaha 650 special has been acting up lately. I recently brought it back to life and it was running really good, then it started running on basically one cylinder. I think I didnt get the rust that was in the gas tank out good enough. Anyways, it was basically running on one cylinder and occasionally when riding it the other one would kick in but only for like one second at a time. It would make a "pop" sound and the bike would get a lot more power, but just for a second, then go back to being really weak. (one time the other cylinder powered up and it rode normally, but this only happened once.) Last time I tried to drive it, it made the pop sound and the side of the engine with the bad cylinder started making a really loud squealing or squeeking sound and it didnt sound too good. It started a few more times after that, the bad cylinder never came back in, and now a few days later I cant get it to start at all. I know it probably really needs the carbs cleaned, as they are probably clogged up with rust, but what could be making that squealing sound? I'm kind of worried...

Any help would be much appreciated.
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does it run?

Did you get your 650 to run? If not let me know. PM me
Well, what was the verdict? Is it running yet?
Tripp - now it is sounding like oil rings on cylinder wall. These old XS 650s have an oil sump in the bottom of the motor, complete with a filter. May be that the oil is not reaching one side...

As far as intermittent running foes - check out your coils.

I would pull the carbs apart and check spark... could be you have a bad coil or a bad charging system,what all did you check before resurecting the bike?
My '76 was making the same pop that you were talking about, turns out trash was in the carb and it was starving the engine for fuel, you might want to look into it.
Running a bike for miles and miles on one piston = not good. Raw gasoline washes the side of the cyl. and rings and can even mix gas into the crankcase oil. The squealing sound might indicate this.
Compression test

Pull off the fuel line on the carb and run it into a bucket off the tank if it flowing good then the tank is okay. I would do a compression test just to see were each cylinder is at. Yamaha dealer can tell you proper P.S.I.
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